Coins are a source of information much used by historians. Elaborately detailed mining landscapes on 16th-century German coins in the National Museum, discovered by the curator of numismatics and brought to the authorís attention, led to this study of early mine-pumping devices. (Images not included - please see Project Gutenberg for illustrations.)
 W. B. Parsons, Engineers and engineering in the Renaissance, Baltimore, 1939. Abraham Wolf, A history of science, technology, and philosophy in the 16th and 17th centuries, New York, 1935; and A history of science, technology and philosophy in the eighteenth century, London, 1938. C. M. Bromehead, "Mining and quarrying to the seventeenth century," in Charles Singer and others, A history of technology, vol. 2, Oxford, 1956.
 According to Parsons (op. cit., footnote 1, p. 629) the introduction of machinery worked by animals and falling water, "radical improvements" of the 15th century, fixed the development of the art "until the eighteenth, and, in some respects, even well into the nineteenth century." Wolf in his History of science ... in the eighteenth century (p. 629, see footnote 1) agrees, saying that "apart from [the steam engine] mining methods remained [during the 18th century] essentially similar to those described in Agricola'